pkg/util/allstacks: wrap the stack traces with debugutil.SafeStack

[arjunmahishi]

The functions Get() and GetWithBuf() internally call runtime.Stack() to fetch the calling go routine's stack trace.

This commit changes the return type of both the function from []byte to debugutil.SafeStack (introduced in #136288). This will ensure that the stack traces generated using these function are not redacted.

Part of: CRDB-15292
Epic: CRDB-37533
Release note: None

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

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[cockroach-teamcity]

This change is 

[arjunmahishi]

pkg/util/debugutil/debugutil.go line 60 at r1 (raw file):

// and only when necessary.
func Stack() SafeStack {
	return SafeStack(debug.Stack())

We don't have to do a an explicit conversion since the return type is already SafeStack. It's ever so slightly faster when we don't do the conversion.

[aa-joshi]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @dhartunian)

[arjunmahishi]

bors r=aa-joshi

[craig]

Build succeeded:

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• local_roachtest
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